The present invention relates to a blood measuring apparatus which performs a blood measurement by using the electrical resistance method.
A related-art blood measuring apparatus is configured as shown in FIG. 5. An aperture 73 configured by a minute hole is disposed between a first chamber 71 and a second chamber 72. An electrode 74 is disposed in the first chamber 71, and an electrode 75 is disposed in the second chamber 72. Diluted blood is contained in the first chamber 71, and a diluting solution is contained in the second chamber 72.
In the related-art blood measuring apparatus in the above-described state, a minute current is caused to flow between the electrodes 74 and 75 through the aperture 73, a resistance change due to blood cells existing between the electrodes 74 and 75 is captured as a change in potential, and a blood measurement (blood cell count) is performed based on the potential change.
The diluted blood which flows from the first chamber 71 into the second chamber 72 through the aperture 73 is carried at an approximately constant distance after flowing into the second chamber 72, by a flow current which is directed toward the aperture 73, and then recirculates to the sensing region due to the electrodes 74 and 75. Therefore, recirculating blood cells exist in the sensing region, and hence it is impossible to capture a resistance change due to only blood cells passing through the aperture 73, so that there is a possibility that the counting operation is erroneously performed.
Moreover, a dead water region where liquid does not flow is produced in the vicinity of the aperture 73. Therefore, air bubbles adhere to a wall portion constituting the sensing region where the aperture 73 is included, and the adhering state of bubbles is varied by a pressure change or a change in liquid flowing state, thereby producing a problem in that such a variation may cause noises during the measurement.
As a related-art technique for, in the blood cell counting measurement, preventing a situation where an error is caused by re-detection due to vortex flow which is formed immediately after the passage through a minute hole, from occurring, there is the back sheath technique (see the right column of page 1 of JP-A-61-159134). When the technique is employed, however, the structure of an apparatus is complicated.